1. Field of the Invention
This invention relates to a surface fastener molded of thermoplastic resin and having a plate-like substrate sheet and a multiplicity of engaging elements standing on a surface of the plate-like substrate sheet and a method for continuously molding the surface fastener by extrusion using thermoplastic resin. More particularly, the invention relates to a surface fastener in which a coarse mesh sheet is embedded in the plate-like substrate sheet and a method for manufacturing the surface fastener.
2. Description of the Related Art
In manufacturing a surface fastener, the technology of molding a plate-like substrate sheet and a multiplicity of engaging elements standing on one surface of the plate-like substrate sheet by extrusion and attaching a core sheet to the plate-like substrate sheet during the molding is disclosed in, for example, U.S. Pat. No. 5,260,015. According to the concept disclosed in this U.S. Patent, molten thermo-plastic resin is extruded to a gap between a rotating drum-shape die wheel, in which a multiplicity of mold disks and a multiplicity of spacer plates are laminated alternately, and a press roller, and the core sheet is introduced between the extruded resin and the press roller. As the core sheet is thus introduced, part of the resin is penetrated into the core sheet by the pressing force of the press roller to integrate with the substrate sheet and, at the same time, part of the resin is filled in hook-element-forming peripheral cavities of the die wheel to mold a multiplicity of hook elements. The resulting surface fastener, in which the core sheet is integrally attached to the substrate sheet at its back surface opposite to the engaging surface, is cooled while traveling through a predetermined angle along the circumferential surface of the die wheel following the rotation of the die wheel, whereupon the molded hook elements are pulled out of the cavities and, at the same time, the substrate sheet is continuously peeled off the circumferential surface of the die wheel.
A continuous injection molding method for continuously manufacturing a surface fastener in which yarns are embedded in a plate-like substrate sheet is disclosed in copending U.S. patent application, Ser. No. 08/359,895 now U.S. Pat. No. 5,571,467. The molding method disclosed in this copending U.S. Application comprises continuously injecting molten resin from an injection die by a predetermined width onto the circumferential surface of a die wheel, which faces the injection die with a predetermined gap and has a multiplicity of hook-element-forming peripheral cavities and a built-in cooler, continuously introducing a plurality of fiber yarns in the direction of rotation of the die wheel across a molten resin outlet of the die wheel and one or more of the fiber yarns traverse by a predetermined width in parallel to the axis of the die wheel, filling the hook-element-forming cavities with part of the molten resin, while rotating the die wheel in the molten resin extruding direction, to embed the yarns in the plate-like substrate sheet to mold a multiplicity of hook elements on the surface of the plate-like substrate sheet, revolving the molded surface fastener through a predetermined angle along the circumferential surface of the die wheel following the rotation of the die wheel, and taking up the hook elements together with the plate-like substrate sheet by positively peeling them off.
In the surface fastener obtained by the manufacturing method disclosed in the above-mentioned U.S. Patent, as is apparent from the object, in an effort to overcome the conventional problem that the conventional type molded surface fastener has a smooth flat back surface so that an adhesive, a cement or the like is difficult to coat over the back surface until the back surface is treated with a special surface treatment, the core sheet is integrally attached to the back surface of the surface fastener to facilitate coating of the adhesive over the back surface and to form a multiplicity of piles or loops as female engaging elements on the back surface. In the resulting surface fastener, the core sheet exists in the plate-like substrate sheet eccentrically to the back-surface side, and part or majority of the plate-like substrate sheet comes out on the back surface.
According to the manufacturing method disclosed in the above-mentioned U.S. Patent, the surface fastener in which the core sheet is embedded in the plate-like substrate sheet eccentrically to the back-surface side is revolved through a predetermined angle along the circumferential surface of the die wheel in one-way rotation and is then positively peeled off the circumferential surface of the die wheel under a predetermined tension. In the case of the substrate-sheet-free surface fastener, since the hook elements molded in the hook-element-forming peripheral cavities of the die wheel have to be positively removed, the plate-like substrate sheet is expanded as a relatively great pulling force is exerted on the plate-like substrate sheet, apart from any deformation of the hook elements.
In the surface fastener manufactured by the method disclosed in the above-mentioned U.S. Patent, since the core sheet is embedded in the substrate sheet eccentrically to the back-surface side with synthetic resin impregnated in part of the core sheet, the back-surface side of the substrate sheet increases its rigidness and, at the same time, becomes less deformable against a pulling force. When the surface fastener molded on the circumferential surface of the die wheel is positively peeled off the circumferential surface as conventional, the substrate sheet is less extendible at the back-surface side, where the core sheet exists, and is more extendible at the front-surface side, where the hook elements exist. Therefore, after completion of the molding, the surface fastener has different lengths at the front and back sides so that the surface fastener is curved convexly at the hook-element side and it is difficult to control the coefficient of extension of the front-surface side, thus resulting in a non-uniform density of hook elements. In use, it is not only inconvenient when such surface fastener is attached to object goods, and a constant engagement strength cannot be achieved to impair the quality of product.
On the other hand, in the surface fastener molded according to the above-mentioned U.S. Patent Application, although it is enough to merely adjust the tension of yarns to be introduced straightly onto the circumferential surface of the die wheel, a traversing mechanism is required to traverse the yarns while being introduced onto the circumferential surface of the die wheel, and it is necessary to control the tension and the traverse width of the yarns with high precision, which makes the manufacturing apparatus complicated to increase the cost of production.